Add const-eval test for #[target_feature(enable = ...)] function calls

tests/ui/consts/const-eval/const_fn_target_feature.rs

@@ -0,0 +1,17 @@
+// only-x86_64
+// compile-flags:-C target-feature=+ssse3
+
+#![crate_type = "lib"]
+
+// ok (ssse3 enabled at compile time)
+const A: () = unsafe { ssse3_fn() };
+
+// error (avx2 not enabled at compile time)
+const B: () = unsafe { avx2_fn() };
+//~^ ERROR evaluation of constant value failed
+
+#[target_feature(enable = "ssse3")]
+const unsafe fn ssse3_fn() {}
+
+#[target_feature(enable = "avx2")]
+const unsafe fn avx2_fn() {}

tests/ui/consts/const-eval/const_fn_target_feature.stderr

@@ -0,0 +1,9 @@
+error[E0080]: evaluation of constant value failed
+  --> $DIR/const_fn_target_feature.rs:10:24
+   |
+LL | const B: () = unsafe { avx2_fn() };
+   |                        ^^^^^^^^^ calling a function that requires unavailable target features: avx2
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0080`.